1. Field of the Invention
The present invention relates to a structure of an actuator which utilizes a mechanical vibration wave generated by vibration generation means such as electro-mechanical energy transducer means including inter alia piezoelectric, electrostrictive and magnetostrictive devices.
2. Related Background Art
Of the actuators which utilize a mechanical vibration wave, a vibration wave motor or ultrasonic wave motor disclosed in Japanese Patent Application Laid-Open No. 29192/1977 has a stator and a movable member in friction contacted with the stator, and at least one of them is constructed by an electro-mechanical energy conversion device or an elastic vibration member containing the electro-mechanical energy conversion means. The movable member is frictionally driven in one direction by the mechanical vibration energy.
In such an ultrasonic wave motor, a vibration due to bending is generated in the vibration member and the movable member is driven by the bending vibration. Thus, when a drive frequency is in the ultrasonic wave range, a vibration mode has a high order and its amplitude is as small as several microns. When a large amplitude is required, the drive frequency goes to the audio frequency range. Since a piezo-electric device which is usually used as the electro-mechanical transducing device uses longitudinal vibration, an electro-mechanical coupling coefficient k is as small as 0.2-0.4 and a piezo-electric constant is as small as 100-300 (.times.10.sup.-12 m/v). Thus, energy conversion efficiency is low.